Catalytic structure



2,965,583 CATALYTIC STRUCTURE Eugene J. Hourlry, Ardmore, and Wilfred M.Adey, 1:301], Pa., assignors to Oxy-Catalyst, Inc., a corporatron ofPennsylvania No Drawing. Continuation of application Ser. No. 442,439,July 9, 1954. This application Oct. 14, 1957, Ser. No. 689,778

13 Claims. (Cl. 252466) This invention is concerned with catalyticstructures and methods for their production.

It has been previously found that catalytic structures of excellentproperties may be prepared by providing a catalytically inert supportwith a thin, adherent, superficial film of a catalytic inorganic oxidesuch as alumina, which then may be impregnated with catalytically activemetals such as platinum, palladium, nickel, etc. Catalytic structures ofthis type and methods for their preparation are described inUnitedStates Patent 2,742,437 of Eugene J. Houdry; in copendingapplication Serial No. 444,275, filed July 19, 1954, now US. Patent No.2,921; 035, of Eugene J. Houdry, entitled Catalyst Manufacture; and inUnited States Patent 2,580,806 of Louis E. Malina. Excellent oxidationcatalysts of high activity anddurability may be prepared using this typeof catalytic structure.

In a preparation of this type of catalyst, one of the chief problems isthat of securing firm adherence of the film of catalytic oxide to thesurface of the inert support. Since the catalytic film should have amaximum thickness of about .015", and is usually of the order of about.0005" to .006" in thickness, the production of a hard, firmly adherentfilm is ofcritical importance with respect to the life of the catalyst.A soft, poorly adherent film is quickly stripped oif the surface of thesupport, rendering the catalyst inactive.

The difliculty of securing adherence of the film varies considerablywith the character of the inert support. It has been found particularlythat a certain degree of surface porosity is of great assistance in thisrespect. Such pores should be quite small, preferably microscopic incharacter, so that the film is deposited on the surface of the supportand not distributed within the pores. It has been found for example,that a support composed of a dense, high quality porcelain, such as thatused in the manufacture of spark plugs, is well adapted to receive thefilm of catalytic oxide. Themicroscopic surface porosity possessed bythis type of porcelain apparently assists greatly in securing firmadherence of the film, andhard, adheren-t films of a variety of oxidessuch as films of catalytic alumina, catalytic. beryllia, silica-alumina,and others, have been produced on this type of support.

On the other hand, the problem of securing adherence of a film of oxideto surfaces which are devoid of porosity such as to the surface ofsmooth metal or glass, has been found to be considerably more difficult.For example, whereas excellent films of catalytic alumina have beenproduced upon a porcelain support of the character described above, ithas proven to be very difficult to secure the firm adherence of a filmof catalytic alumina to a metal or glass surface. In the case of a metalsupport, the problem of maintaining adherence of the film is aggravatedby the fact that, due to the large difference in the coeificients ofexpansion of the metal and the catalytic film, the film of oxide tendsto become dislodged in use due to repeated expansions and contractionscaused by alternate heating and cooling of the catalyst structure.

It has now been found that hard, adherent catalytic films may beproduced upon smooth, non-porous surfaces, such as metal, glass orplastic surfaces, by using certain combinations of catalytic oxides,namely, mixtures containing catalytic alumina and catalytic beryllia ormixtures containing catalytic alumina and catalytic zirconia. While noneof these oxides in themselves will produce a satisfactory film upon thesurface of such a support, the mixtures of alumina with beryllia or withzirconia produce excellent results. Apparently these combinations havethe ability to promote Wetting of the surface, thus producing uniformadhesion. At the same time the composite film possesses hard,non-chalking properties which generally are chiefly characteristic offilms composed of straight. alumina.

While any smooth surface substantially devoid of porosity may beprovided with a catalytic coating of these oxides, such as smooth metal,glass or plastic surfaces, care should be taken that the surface withwhich the film is in contact does not contain substances detrimental tothe catalytic activity of the film. Some metal alloys containing iron orcopper, for example, particularly at high temperatures, have a tendencyto destroy the catalytic activity of catalysts prepared with theseoxides. Determination of the suitability of the support in this respectcan be determined by simply preparing a sample of the desired catalystand testing its activity.

The proportions of alumina and beryllia. or of alumina and zirconia mayvary considerably. While generally the best results are obtained byemploying equi-molecular proportions of alumina with the other oxidevery acceptable results are obtained when one oxide is present inconsiderableexcess of the other. Generally speaking, the mole ratio Al O:BeO or of A1 O :ZrO should lie within the range of 1:10 to 10:1 andpreferably in the range from 1:5 to 5:1.

As is well known in the art, not all forms of these oxides arecatalytically active, some forms possessing little or no catalyticproperties. The catalytic form of these oxides is characterized by aminute, porous structure which possesses a large internal surface area.In the case of alumina for example, the so-called alpha alumina, orcorundum, possesses little internal pore volume and is catalyticallyinert. The so-called gamma alumina on the other hand is characterized bya large internal surface area and is recognized as being the catalyticform of alumina, The catalytic forms are generally preparedsynthetically by precipitation of a gel from a solution, followed bydrying and then heating the gel at a controlled temperature to removehydrated water. Catalytic alumina, for example, may be preparedsynthetically by precipitating an alumina gel from a solution of analuminum salt, drying the gel and thereafter heating carefully at atemperature preferably no higher than about 1500" F. to expel thehydrated water and to produce the substantially anhydrous or partiallyhydrated oxide which is the catalytically active or so-called adsorbtiveform of alumina. Catalytic beryllia or zirconia may be preparedsynthetically in a similar manner. Catalytic alumina may also beprepared from the naturally occurring bauxite, which contains hydratedalumina, by removal of impurities such as iron and silicates which itcontains and heating at a controlled temperature. This heating of thehydrated oxide from which the catalytic form is prepared, to drive offthe hydrated water, is ordinarily termed activation.

The mixture of oxides is applied to the surface of the insert support bycontacting the support, preferably by dipping, with a slurry of amixture of the oxides in finely divided form in a liquid vehicle.Preferably, the film is deposited by the method described in UnitedStates Patent 2,580,806 of Louis E. Malina. According to this method, aslurry is prepared consisting of a mixture of finely divided alumina andberyllia or of alumina and zirconia suspended in an aqueous solution ofa compound decomposable into a catalytic inorganic oxide. A slurry ofeither of these mixtures of oxides suspended in a concentrated aqueoussolution of a heat-decomposable aluminum salt, especially aluminumnitrate, provides a particularly desirable medium from which to depositthe catalytic film.

From such a slurry, the film is deposited upon the support preferably bydipping it into the slurry, draining, drying to evaporate free moisture,and then heating at a temperature below about 1500 F. to decompose thecompound originally present in solution into its catalytic oxide. Forexample, by dipping a metal support into a slurry consisting of finelydivided catalytic alumina and beryllia suspended in a saturated aqueoussolution of aluminum nitrate, a uniform deposit is produced on thesurface of the metal; After drying, this deposit consists of a film ofcatalytic alumina and beryllia containing aluminum nitrate crystalsdeposited during evaporation of the free moisture. Upon heating thisfilm to about 500 F. the aluminum nitrate decomposes into catalyticalumina.

In order to insure the production of a film of maximum hardness and ofexcellent adherence to the surface of the non-porous support, preferablythe oxides are reduced to an extremely finely divided condition beforebeing deposited on the surface of the support. This may be accomplishedby subjecting them, either separately or in admixture, to a severecolloidization operation preferably in an attrition type colloid mill,using a wet grinding technique with the oxide suspended in an aqueousvehicle. A detailed description of this type of colloidizing operationis given in copending application Serial No. 444,275, filed July 19,1954, by Eugene J. Houdry for Catalyst Manufacture.

The thickness of the catalytic film is of great importance. Essentially,the film of catalytic oxide should be very thin, and should not in anycase exceed a thickness of about .015". Films of greater thickness thanthis have a strong tendency to crack and to flake off the support.Preferably, the film is considerably thinner than .015" and in general,may have a thickness of as little as about .0001" and, for best results,not in excess of about .006". When using a metal support, because of thewide differences in the coefiicients of expansion of the metal and ofthe oxide, filmthicknesses even considerably less than .006" arepreferred, the most satisfactory results with a metal support beinggenerally obtained with films having a thickness of from about .0003" to.0015".

Alumina-beryllia or alumina-zirconia films having a thickness of theorder described above may be produced satisfactorily by using the filmapplying techniques generally outlined above and which will be describedmore specifically in the examples which follow. By dipping a metalsupport for example, in a slurry consisting of a mixture of finelydivided alumina and beryllia suspended in an aqueous solution ofaluminum nitrate, a film approximately from .0001" to .0005 thick isdeposited during the first dipping and drying operation and this filmthickness can be increased by substantially the same amount by eachsubsequent dipping and drying operation. For most applications, from oneto three successive coatings is suflicient.

The alumina-beryllia or. alumina-zirconia film provides an excellentbase or carrier for finely divided catalytically active metals toproduce catalytic structures of outstanding properties. In particular,oxidation catalysts of superior flexibility, activity and durability maybe produced by impregnating such a film with finely divided metals suchas platinum, ruthenium, palladium, silver, chromium, copper, cobalt andnickel and combinations of these metals. Particularly excellent resultsare obtained with the use of platinum. Impregnation may be accomplishedby methods well known in the art such as by impregnating the dry oxidefilm with an aqueous solution of a salt of the desired metal, and thendecomposing the salt into the catalytically active metal, which isthereby deposited upon and within the oxide film in finely dividedcondition. The film may be impregnated with platinum, for example, byimmersing the support carrying the film in a solution of chloroplatinicacid (H PtCl bH O) drying and then heating to decompose the platinumsalt thus depositing metallic platinum in finely divided form..

A 22 gage nickel-20% chromium) resistance wire was employed as the inertsupport. This wire, in the form of a closely wound fiat coil was dippedinto a slurry prepared as follows.

A calcined, catalytic grade alumina powder ground through about 300mesh, manufactured by the Harshaw Chemical Company, was employed, thisalumina having the following analysis:

A1 0 90.2% by weight. Na O 0.43% by weight. Fe O Less than 0.36% Y byweight. SiO Less than 018%" by'weight. I Combined H O 9.1% by weight. j

This alumina was mixed'with water in the proportion of 5 kilograms ofalumina powder in sufiicient water to give 8 litres of slurry. ,Thiswater-alumina mixture was passed repeatedly through an attritiontype'colloid mill, being careful to maintain uniformity of the slurry byagitation. The colloid mill employed is manufactured by the Troy Engine& Machine Company, of Troy, Pennsylvania. It consists of a rotating discand a stationary disc between which the slurry is pumped, withadjustable means for forcing these discs toward one another. Therotating disc revolves at a speed of 20,000 r.p.m. while the slurry isforced between it and the stator thereby subjecting the particles tohydraulic shear.

The original mixture was passed through this mill a total of eighttimes. With each successive pass through the mill, the adjustment forincreasing the force with which the discs are biased toward one'anotherwas increased until colloidization was completed to the desired extent.The end-point of the colloidization procedure was determined by the factthat the alumina-water slurry (containing approximately equal weights ofwater and alumina) underwent a rather remarkable increase in viscosity,acquiring a smooth semi-self-sustaining consistency and showing verylittle tendency to separate into two phases even on prolonged standing.Particle size studies on this slurry. by sedimentation technique andelectron microscope examination shows that approximately 50% of the masshas been reduced to a particle size below one micron while there is lessthan a negligible 'weight percentage of particles of greater than 20'microns in size. The specificsurface of the alumina particles calculatedfromparticle' size distribution curves is of the order orfsaooo squarecentimeters per cubic centimeter of packedvolume assuming sphericalparticles and considering only the outside geometric area: ofeach-particle (that is, neglecting internal pore area). 1 j

This beryllia was mixed with water and subjected to approximately thesame type of colloidization operation as described above with referencetothe alumina.

At the end of the colloidization operatiomthe wateralumina slurrycontained about 44% solids by weight and the beryllia-water slurrycontainedabout 56% solids by weight. These two slurries were mixedtogether and with aluminum nitrate crystals in the followingproportions, which in the finished film produces substantiallyequi-molecular proportions of alumina and beryllia:

43.5 gms. BeO-water slurry (56% solids) 228.0 gms. Al O -water slurry(44% solids) 16.0 gms. AI(NO .9H O crystals The coil of resistance wirewas dipped into this mixture, removed, drained, and the excess slurryremoved by vigorous shaking. The coil was connected to a source ofelectric current and heated electrically to incipient red heat about1000 F. over a period of 1 to 2 minutes by en vigorously, and thenheated electrically to dry the film.

Thefilmthus produced, about .001" in thickness, was firmly adherent tothe surface of the wire and was quite hard and resistant to chalking. Totest its ability to withstand repeated expansions and contractions ofthe wire, the coil containing the catalytic coating was heated to redheat and then cooled 10,000 times with no detectable deterioration inthe catalytic coating. Although the coated wire could not be sharplybent without dislodging the alumina-beryllia film, it could be flexedconsiderably without damaging the film.

An oxidation catalyst of excellent activity was prepared by dipping thecoil containing the alumina-beryllia film into an aqueous solution ofchloroplatinic and containing 1% of platinum by weight. The coil wasagain heated slowly by passing electric current through the wire,bringing the coil to red heat. Complete decomposition of the platinumsalt into metallic platinum was accomplished by heating the coil in agas flame to bright redness. The catalytic structure thus produced has agreat many applications as an oxidation catalyst and is particularlyuseful in catalytically oxidizing trace constituents in a gas stream,such as traces of organic smokes, and small concentrations of organicvapors such as those given off in the roasting or baking of meat orother food products.

Example 11 5.3 gms. beryllia-water slurry (47.2% solids) 35.0gmsaIumina-water slurry (56.4% solids) 3.2% aluminum nitrate crystals(Al(N .9H O) 8.6 gms. water i The film of catalytic oxides, after dryingand decom- "position of the aluminum nitrate was likewise hard andfirmly adherent to the surface of the wire making up the coil. I

Example III The procedure outlined in Example .I was again repeatedexcept that in this case the proportion of beryllia was increased overthat used in Example I. In this case the slurry in which the coil wasdipped for depositing the film was compounded as follows:

The catalytic film produced using this slurry was also hard and firmlyadherent to the surface of the metal coil.

Example IV A thick sheet of a metal alloy sold under the trade nameInconel X was employed as the support. This alloy has the following.approximate analysis: 75% nickel, 15% chromium, 7% iron, 2.5% titanium,with small amounts of columbium, aluminum, silica and manganese. Thesame technique described in Example I were used. After dipping, it wasallowed to drain, was dried and then heated to about 500 F. to decomposethe aluminum nitrate into alumina. The alurnina-berylliafilm thusproduced on the surface of the metal sheetwas about .0005 in thickness,and was hard and firmly adherent to the surface of the metal. It was noteasily scratched and was not removed from the surface by vigorous fingerrubbing. r

The alumina-beryllia film on the surface of the metal sheet wasimpregnated with about 1% to 2% by weight (based on the weight of thealumina-beryllia film) of platinum by dipping into a solution ofchloroplatinic acid, after which the sheet was heated to decompose theplatinum salt into metallic platinum. The resultant catalytic structure,when heated to about 700 and then exposed to city gas flowing over thesurface of the catalytic film, caused the metal sheet to glow at redheat due to the oxidation of the city gas at the surface of the film inthe presence of atmospheric air.

Example V The procedure outlined in Example IV was repeated except thatan additional coating of alumina-beryllia was applied over the first,increasing the total thickness of the film to .001". This film, whenimpregnated with platinum in the manner described in Example IV provedto be an equally effective oxidation catalyst.

Example VI A length of resistance wire, similar to that used in ExampleI was provided with a zirconia-alumina film using the same generalcoating techniques outlined in Example I. In this case the slurry inwhich the coil was dipped to deposit the film was compounded as follows:

45 gms. ZrO -Water slurry (69.0% solids) 44 gms. Al O -water slurry(56.4% solids). 4 gms. Al(NO .9H O crystals Example VII Using the samegeneral procedure outlined in Example I, a length of resistance wire wasprovided with a film 7 of catalytic oxides. The slurry in which the coilwas dipped to deposit the film was compounded as follows:

38.8 gms. ThO -water slurry (68.0% solids) 17.8gms. ZrO -water slurry(69.0% solids) 20.0 gms. Al O -water slurry (56.4% solids) 4.0 gms.Al(NO .9H crystals cases to include other catalytic oxides such asthoria in I the mixture of alumina with beryllia or with zirconia toproduce a hard, adherent film on a non-porous surface.

Example VIII The procedure outlined in Example VII was repeated exceptthat in this case a film was produced containing a relatively smallamount of alumina, the alumina being introduced solely in the form ofaluminum nitrate crystals. The slurry from which the film was depositedupon the surface of the Nichrome wire was compounded as follows: i

38.8 gms. ThO =water slurry (68.0% solids) 17.8 grns. ZrO ==water slurry(69.0% solids) 6.0 fims. Al(NO .9I-I O crystals A hard, adherent,uniform film was produced, having a thickness of about .0005". Such astructure, in which the alumina-zirconia-thoria film was impregnatedwith platinum by the procedure outlined in Example I proved to be anexcellent oxidation catalyst.

Attempts to produce satisfactory catalytic coatings using alumina,beryllia or zirconia alone, or other oxides alone or in combination,were unsuccessful. With alumina alone for example, using the samegeneral techniques described above, adherence to the surface of themetal was poor, and where it was possible to produce a film at all, itwas non-uniform and flaky in character. Using beryllia alone, areasonably uniform film was produced. However, the beryllia film wassoft and powdery and could be easily removed from the surface of themetal by light finger rubbing. Similarly unsuccessful attempts toproduce a hard, adherent film were experienced using other combinationsof oxides such as silica-alumina, magnesia-alumina, thoria-alumina andceria-alumina combinations.

The invention makes possible the provision of catalytic structures ofexcellent properties suitable for use in many practical applications. Aresistance element for example, coated with the film of beryllia andalumina and thereafter impregnatedwith a metal such as platinum,provides an excellent oxidation catalyst which has the advantage thatthe catalytic surface may be very quickly heated to the requiredreaction temperature by passing an electric current through the metalresistance element, thereby heating the catalytic film on its surfacedirectly. This type of catalytic structure is the subject of UnitedStates Patent 2,731,641 of Eugene J. Houdry and Wilfred R. Adey. As anoxidation catalyst, such a structure may be employed to oxidize traceconstituents in a gas stream such as traces of organic smoke, or organicgases or vapors. A fiat coil of resistance wire such as that describedin Example I provided with a film of alumina-beryllia of about .001" inthickness and impregnated with about 1% to 2% of a metal such asplatinum or palladium, has been used very successfully for the oxidationof smoke, greases and traces ofodorous organic material which are givenoff during the cooking of food, such as during the baking or roasting ofmeat. Oxidation of these constituents is effected by passing the aircontaining the trace contaminant over the catalyst heated electricallyto a temperature of the order of about 700 F. to 800 F. The eliminationof such constituents is substantially complete.

The invention also makes it possible to directly. coat with catalyst theinner wallsof metal lined combustion chambers, such as the type used injet aircraft. The presence of the catalytic coating on the wall of thecombustion chamber tends to improve combustion efficiency close to thesurface of the wall where, because of the lower temperatures, combustionefficiency is relatively poor.

Many other applications are possible for this type of structure inpromoting oxidation and other types of reactions, and it is not intendedthat the invention be limited to the particular applications described,nor to the specific examples which are given for the purpose ofillustration, the invention being limited only by the scope of theappended claims.

This application is a continuation of copending application Serial No.442,439, filed July 9, 1954, now abandoned, by Eugene J. Houdry andWilfred M. Adey for Catalytic Structure.

We claim:

1. A catalytic structure comprising a support of a material which isessentially devoid of surface porosity and is a member selected from thegroup consisting of metal and glass, provided with a thin, adherent,superficial film comprised of a mixture of catalytic alumina withanother oxide selected from the group consisting of catalytic berylliaand catalytic zirconia, the mole ratio of the catalytic alumina to saidother oxide being in the range of from 1:10 to 10:1.

2. A catalytic structure comprising a support of a material which isessentially devoid of surface porosity and is a member selected from thegroup consisting of metal and glass provided with a thin, adherent,superficial film comprised of a mixture of catalytic alumina andcatalytic beryllia.

3. A catalytic structure comprising a support of a material which isessentially devoid of surface porosity and is a member selected from thegroup consisting of metal and glass provided with a thin, adherent,superficial film comprised of a mixture of catalytic alumina withanother oxide selected from the group consisting of catalytic berylliaand catalytic zirconia, the mole of the catalytic alumina to said otheroxide being in the ratio of from 1:10 tol0:l and said film beingimpregnated with a finely divided catalytically active metal.

4. A catalytic structure adapted for promoting oxidation reactioncomprising a support of a material which is essentially devoid ofsurface porosity and is a member selected from the group consisting ofmetal and glass provided with a thin, adherent, superficial filmcomprised of a mixture of catalytic alumina withanother oxide selectedfrom the group consisting of catalytic beryllia and catalytic zirconia,the mole ratio of of the catalytic alumina to said other oxide being inthe range of from 1:10 to 10:1 and said film being impregnated with afinely divided catalytically active metal selected from the groupconsisting of platinum, ruthenium, palladium, silver, chromium, copper,nickel, cobalt and mixtures thereof.

5. A catalytic structure comprising a support of a material which isessentially devoid of surface porosity and is a member selected from thegroup consisting of metal andglass providedwith an adherent, superficialfilm, comprised of a mixture of catalytic alumina with another oxideselected from the group consisting of catalytic beryllia and catalyticzirconia, having a thickness of from .0001" to .006", the mole ratio ofthe catalytic alumina to said other oxide being in the range of from 6.A catalytic structure comprising a support of a material which isessentially devoid of surface porosity f i mb 9? iii l f l l". se i t nsmetal and glass provided with an adherent, superficial film comprised ofa mixture of catalytic alumina with another oxide selected from thegroup consisting of catalytic beryllia and catalytic zirconia, the moleratio of the catalytic alumina to said other oxide being in the range offrom 1:10 to :1 and said film having a thickness of from .0001 to .006"and being impregnated with a finely divided catalytically active metal.

7. A catalytic structure adapted for promoting oxidation reactioncomprising a support of a material which is essentially devoid ofsurface porosity and is a member selected from the group consisting ofmetal and glass provided with an adherent, superficial film comprised ofa mixture of catalytic alumina with another oxide selected from thegroup consisting of catalytic beryllia and catalytic zirconia, the moleratio of the catalytic alumina to said other oxide being in the range offrom 1:10 to 10:1 and said film having a thickness of from .0001" to.006", and being impregnated with a finely divided catalytically activemetal selected from the group consisting of platinum, ruthenium,palladium, silver, chromium, copper, nickel, cobalt and mixturesthereof.

8. A catalytic structure comprising a support of a material which isessentially devoid of surface porosity and is a member selected from thegroup consisting of metal and glass provided with a thin, adherent,superficial film comprised of a mixture of catalytic alumina withanother oxide selected from the group consisting of catalytic berylliaand catalytic zirconia, the mole ratio of the catalytic alumina to saidother oxide being in the range of from 1:10 to 10:1 and said supportbeing substantially free from metals detrimental to the activity of thecatalytic film.

9. A catalytic structure comprising a metal support having a smooth,essentially non-porous surface provided with a thin, adherent,superficial film comprised of a mixture of catalytic alumina andcatalytic beryllia, the mole ratio of the catalytic alumina to thecatalytic beryllia being in the range of from 1:10 to 10:1 and saidsupport being substantially free from metals detrimental to the activityof the catalytic film.

10. A catalytic structure comprising a metal support having a smooth,essentially non-porous surface provided with a thin, adherent,superficial film comprised of a mixture of catalytic alumina withanother oxide selected from the group consisting of catalytic berylliaand catalytic zirconia, the. mole ratio of the catalytic alumina to saidother oxide being in the range of from 1:10 to 10:1 and said film beingimpregnated with a finely divided catalytically active metal, saidsupport being substantially free from metals detrimental to the activityof the catalytic film.

11. A catalytic structure adapted for promoting oxidation reactionscomprising a metal support having a smooth, essentially non-poroussurface provided with a thin, adherent, superficial film comprised of amixture of catalytic alumina with another oxide selected from the groupconsisting of catalytic beryllia and catalytic zir: conia, the moleratio of the catalytic alumina to said other oxide being in the range offrom 1:10 to 10:1 and said film being impregnated with a finely dividedcatalytically active metal selected from the group consisting ofplatinum, ruthenium, palladium, silver, chromium, copper, nickel, cobaltand mixtures thereof, said support being substantially free from metalsdetrimental to the activity of the catalytic film.

12. A structure in accordance with claim 11 in which said film has athickness of from .003" to .0015".

13. A catalytic structure comprising a metal support having a smooth,essentially non-porous surface provided with an adherent, superficialfilm comprised of a mixture of catalytic alumina and catalytic beryllia,said alumina, said beryllia and said aluminum nitrate being in an amountto provide a film containing a mole ratio of alumina to beryllia in therange of from 1:10 to 10:1 and said film having a thickness of fromabout .0003 to .0015" and being impregnated With from .2% to 5% byweight of platinum based on the weight of the aluminaberyllia film, saidsupport being substantially free from metals detrimental to the activityof the catalytic film.

References Cited in the file of this patent UNITED STATES PATENTS

1. A CATALYTIC STRUCTURE COMPRISING A SUPPORT OF A MATERIAL WHICH ISESSENTIALLY DEVOID OF SURFACE POROSITY AND IS A MEMBER SELECTED FROM THEGROUP CONSITING OF METAL AND GLASS, PROVIDED WITH A THIN, ADHERENT,SUPERFICIAL FILM COMPRISED OF A MIXTURE OF CATALYTIC ALUMINA WITHANOTHER OXIDE SELECTED FROM THE GROUP CONSISTING OF CATALYTIC BERYLLIAAND CATALYTIC ZIRCONIA, THE MOLE RATIO OF THE CATALYTIC ALUMINA TO SAIDOTHER OXIDE BEING IN THE RANGE OF FROM 1:10 TO 10:1.
 4. A CATALYTICSTRUCTURE ADAPTED FOR PROMOTING OXIDATION REACTION COMPRISING A SUPPORTOF A MATERIAL WHICH IS ESSENTIALLY DEVOID OF SURFACE POROSITY AND IS AMEMBER SELECTED FROM THE GROUP CONSISTING OF METAL AND GLASS PROVIDEDWITH A THIN, ADHERENT, SUPERFICIAL FILM COMPRISED OF A MIXTURE OFCATALYTIC ALUMINA WITH ANOTHER OXIDE SELECTED FROM THE GROUP CONSISTINGOF CATALYTIC BERYLLIA AND CATALYTIC ZIRCONIA, THE MOLE RATIO OF OF THECATALYTIC ALUMINA TO SAID OTHER OXIDE BEING IN THE RANGE OF FROM 1:10 TO10:1 AND SAID FILM BEING IMPREGNATED WITH A FINELY DIVIDED CATALYTICALLYACTIVE METAL SELECTED FROM THE GROUP CONSISTING OF PLATINUM, RUTHENIUM,PALLADIUM, SILVER, CHROMIUM, COPPER, NICKEL, COBALT AND MIXTURES THEREOF